Existing drive systems for rolling curtains/doors employ rollers on the door edges which engage surfaces of a track in a door guide positioned on a pair of opposite sides of a door opening. The door (curtain) may be a vertical door, which is deployed from top to bottom across a door opening; a side-coiling curtain, which is deployed sideways from left-to-right (or right-to-left) across the door opening; or a horizontal curtain, which is deployed across a horizontal opening such as, for example, a floor opening containing an escalator.
In such doors, the rollers provide a rolling engagement along the guide tracks. The door (curtain) itself is typically comprised of interlocking, loosely-fitted slats, which are locked together at their ends to maintain the slats in alignment with each other.
A problem can arise with any door traversing a significant space in that, in a high wind or other load condition, such as during a storm, a wind force against the door can create a bowed condition at an unsupported portion of the door slats, which bowing has the effect of creating an unwanted locking condition between the rollers and a surface of the tracks. Such condition can have the effect of prohibiting or restricting rolling movement of the door, depending on the wind load.
Even during regular load conditions, some movement or “play” exists between the rollers and the guide track such that the front faces of the rollers will contact the edges of the guide tracks and cause friction there-between. This condition limits the closing and opening speeds of the door.
Typically, for horizontal and side-coiling curtains, (and in instances where vertical curtains require constant operating speed), a pusher, in particular, a cog, is used to move the curtain between the opened and closed positions. In conventional systems, this is typically accomplished by positioning the cog for engagement with surfaces of the door slats to deploy and retract the curtain with respect to a coil that holds the undeployed portion of the curtain. In systems that use direct engagement of the pusher cog with the slats, wear on the slat surfaces is created and unwanted noise generated due to the striking of the cog with the slats as the curtain is moved between its opened and closed positions. To account for the wear to the slats, the metal gauge used to manufacture the slats need to be of a sufficient thickness. This adds to the cost and weight of the curtain.